Interesting, from the same article:

The county did not spend any money on the study, but officials at King County's Wastewater Treatment Division said they were happy to cooperate because they expected the results to reinforce their message: What goes down the drain has to come out somewhere. That goes both for pesticides and industrial chemicals as well as vanilla and cinnamon. "It's an ability to look at a whole population's behavior through one pipe," said Randy Schuman, a county science and technical support manager who helped arrange the wastewater testing.

Keil's findings present a light side of what scientists say is potentially a serious situation. Scientists at the U.S. Geological Survey and other agencies have documented that antibiotics, contraceptives, perfumes, painkillers, antidepressants and other substances pass through the sewage system into waterways.

King County researchers several years took caffeine measurements to try to learn whether the city's coffee drinking habits had any effect on the sound. Caffeine was found in more than 160 of 216 samples in water as deep as 640 feet.